Step 1: Prepare the Beef

1. Season the Beef: Start by seasoning the beef tenderloin tips with salt and pepper on all sides. This will help enhance the natural flavor of the beef.
2. Heat the Pan: In a large skillet or sauté pan, heat the olive oil over medium-high heat. You want the pan to be hot so that the beef sears quickly and develops a nice brown crust.
3. Sear the Beef: Add the beef tips to the pan in a single layer. Avoid overcrowding the pan to ensure the beef sears properly. Cook the beef for 2-3 minutes on each side, or until it is browned and caramelized. Once browned, remove the beef tips from the pan and set them aside.

Step 2: Prepare the Mushroom Gravy

1. Cook the Onions: In the same skillet, add the chopped onion and cook over medium heat for 2-3 minutes, stirring occasionally, until softened and translucent.
2. Add the Mushrooms: Add the sliced mushrooms to the pan and cook for 5-7 minutes, until the mushrooms release their moisture and become golden brown. Stir occasionally to ensure even cooking.
3. Add the Garlic: Stir in the minced garlic and cook for an additional 30 seconds, until fragrant.
4. Make the Roux: Sprinkle the flour over the mushroom mixture and stir to combine. This will create a roux that will help thicken the gravy. Cook the roux for 1-2 minutes, stirring frequently, to eliminate the raw flour taste.
5. Deglaze the Pan: Slowly pour in the beef broth, stirring constantly to combine and scrape up any browned bits from the bottom of the pan. This will add even more flavor to the gravy.
6. Simmer the Gravy: Stir in the heavy cream, Worcestershire sauce, and thyme. Bring the mixture to a simmer and cook for 5-7 minutes, until the gravy thickens and reduces slightly. Taste the gravy and adjust the seasoning with salt and pepper as needed.

Step 3: Combine the Beef and Gravy

1. Return the Beef to the Pan: Add the seared beef tips back into the pan with the mushroom gravy. Stir gently to coat the beef with the sauce.
2. Simmer: Let the beef simmer in the gravy for 5-7 minutes, or until it reaches your desired level of doneness. The beef should be cooked through but still tender.
3. Final Touch: If the gravy is too thick, you can add a splash more beef broth or cream to reach your desired consistency.

Step 4: Serve and Garnish

1. Serve: Transfer the Beef Tenderloin Tips in Mushroom Gravy to a serving platter or individual plates.
2. Garnish: Sprinkle freshly chopped parsley on top for a burst of color and freshness.
3. Enjoy: Serve immediately, either on its own or with your favorite side dishes.